Dissolution of barium sulfate scale deposits by chelating agents

The occurrence of barium sulfate scale (BaSO4) is a severe problem and its associated environmental concerns in oil and gas production worldwide will cause considerable production losses. Chemical dissolution will create a ne w direction for controlling the scale deposits by chelating agents, which f orm strong complexes with metal ions in solution. Chemical dissolvers based on the aminoacetate group can be considered strong chelating agents for ba rium ions. Diethylenetrinitrilopentaacetic acid (DTPA) and ethylenedinitril otetraacetic acid (EDTA) are two major chelating agents used for the dissol ution experiments. The kinetic studies for the dissolution reaction of scal e-forming materials will be presented. Dissolution follows the first-order kinetics for the stirred system. The activation energies obtained in the st irred system of DTPA and EDTA, 9.59 and 9.31 kcal/mol, respectively, sugges ted that mass transfer is not the controlling factor. In this system, the s urface reaction is considered as the rate-controlling step in the dissoluti on process. This study includes the dissolution kinetics in the aqueous sys tem and surface! phenomena on the solid. Surface phenomena such as morpholo gy and surface pitting have been investigated by scanning electron microsco py. The morphology changes as a function of dissolution time.